The most frequently used polymers in the preparation of resilient flooring are polyvinyl chloride (PVC) and vinyl chloride copolymers, principally copolymers of vinyl chloride and vinyl acetate. The art of compounding and processing PVC-based compositions is well understood.
The processing and forming of PVC-based compositions is greatly facilitated by the use of plasticizing additives. Esters of phthalic acid, such as di-2-ethylhexyl phthalate (DOP), are commonly used. The use of such plasticizing additives also facilitates the incorporation of high levels (up to about 80% by weight) of fillers and pigments and affords finished compositions with an acceptable degree of flexibility and resiliency.
PVC resins generally require the use of stabilizing additives to prevent discoloration resulting from thermally induced decomposition of the resin during processing. The use of stabilizing additives also helps to prolong the useful life of a PVC-based product by continuing to prevent degradation induced by heat or by light during the service life of the product. These stabilizing additives typically include metal containing compounds such as the barium, zinc, and cadmium salts of organic acids (e.g. stearic acid) and organotin compounds.
The necessary use of these additive materials can create a variety of undesirable problems in composite flooring structures. As one example, in a flooring structure in which a plasticized PVC composition is protected by a clear unplasticized coating, migration of the plasticizer from the PVC composition into the protective clear coating can soften the coating and thereby lessen its protective capabilities.
A second undesirable situation arises from the need to use metal-containing additives. The forced combustion of PVC-based compositions, as in an incinerator, results in the creation of volatile and hazardous metal-containing pollutants.
Other undesirable conditions are also created when PVC-based compositions burn as might occur in a fire situation. The combustion of such materials can result in the evolution of dense smoke which can contribute to a hazardous conditions at times when visibility is important. Furthermore, halogen-containing products of combustion, such as hydrogen chloride, can be formed, thereby adding a further element of hazard to a fire situation.
Halogen-free floor coverings have been proposed such as in White, U.S. Pat. No. 3,336,254. However, such a halogen-free floor covering required an unsaturated elastomer component to impart resiliency and fibers to strengthen and reinforce the floor tile as well as enhance dimensional stability and impact strength.
Schumacher, U.S. Pat. No. 4,430,468, discloses a halogen-free, filled, thermoplastic polymer composition for use in automotive carpets and the backing of the fabric or scrim used to cover the interior panels of an automobile. There is no suggestion in Schumacher of using the composition to form a resilient floor covering. In fact, not all of the compositions disclosed in Schumacher are useful in resilient floor coverings.
It is an object of the invention to provide a halogen-free resilient flooring, thereby eliminating the potential for the formation of hydrogen chloride for other halogenated products and combustion when the floor covering is burned.
It is a further object to provide a flooring which significantly lowers the density of smoke involved in a test such as the NBS Smoke Chamber when compared to floor coverings having comparable PVC compositions.
It is a still further object to provide a flooring free of stabilizing additives containing metals such as tin, zinc, cadmium, and barium. Thereby eliminating metal-containing combustion products.
It is another object of the invention to provide a flooring free of liquid plasticizing compounds such as di-2-ethylhexyl phthalate, thereby eliminating migration of such plasticizer.